首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   551篇
  免费   44篇
  国内免费   1篇
化学   479篇
力学   3篇
数学   46篇
物理学   68篇
  2024年   2篇
  2023年   15篇
  2022年   22篇
  2021年   55篇
  2020年   30篇
  2019年   18篇
  2018年   17篇
  2017年   13篇
  2016年   32篇
  2015年   26篇
  2014年   24篇
  2013年   24篇
  2012年   37篇
  2011年   34篇
  2010年   14篇
  2009年   8篇
  2008年   30篇
  2007年   29篇
  2006年   16篇
  2005年   28篇
  2004年   17篇
  2003年   20篇
  2002年   13篇
  2001年   10篇
  2000年   4篇
  1999年   5篇
  1998年   1篇
  1997年   2篇
  1996年   4篇
  1993年   1篇
  1992年   1篇
  1991年   3篇
  1990年   4篇
  1989年   5篇
  1988年   1篇
  1987年   5篇
  1986年   3篇
  1985年   2篇
  1984年   3篇
  1983年   3篇
  1982年   6篇
  1981年   2篇
  1980年   2篇
  1979年   2篇
  1978年   1篇
  1977年   1篇
  1970年   1篇
排序方式: 共有596条查询结果,搜索用时 171 毫秒
171.
This study was conducted to determine heavy metals concentrations in tissues of 94 birds belonging to different species from coastal areas of Naples and Salerno (Southern Italy) in order to provide baseline data concerning trace element levels in wild birds living in or close to an area characterized by high anthropogenic impact. Additional aim of this study was to verify if diet influenced metal accumulation, so birds were classified as birds of prey, fish eating birds and insectivorous birds.  相似文献   
172.
A novel method for the mild photoredox‐mediated tandem radical acylarylation and tandem acylation/semipinacol rearrangement has been developed. The synthesis of highly functionalized ketones bearing all‐carbon α‐ or β‐quaternary centers has been achieved using easily available symmetric aromatic carboxylic anhydrides as the acyl radical source. The method allows for a straightforward introduction of the keto functionality and concomitant construction of molecular complexity in a single operation.  相似文献   
173.
174.
175.
176.
Our work proposes to study the conuclear image of a substructural logic and in particular to investigate the relationship between a substructural logic and its conuclear image. We analyze some axioms familiar to substructural logics and we check if they: (a) are preserved under conuclear images, (b) never hold in a conuclear image, or (c) are compatible with conuclear images but are not necessarily preserved under conuclear images. Moreover, we prove that the conuclear image of any substructural logic has the disjunction property. We finally give a sufficient condition in order that an inequality is preserved under conuclear images and observe that if we slightly relax this condition, we meet counterexamples of inequalities that are not preserved under conuclear images.  相似文献   
177.
178.
179.
A semisynthetic approach to novel lipid A derivatives from Escherichia coli (E. coli) lipid A is reported. This methodology stands as an alternative to common approaches based exclusively on either total synthesis or extraction from bacterial sources. It relies upon the purification of the lipid A fraction from fed‐batch fermentation of E. coli, followed by its structural modification through tailored, site‐selective chemical reactions. In particular, modification of the lipid pattern and functionalization of the phosphate group as well as of the sole primary hydroxyl group were accomplished, highlighting the unusual reactivity of the molecule. Preliminary investigations of the immunostimulating activity of the new semisynthetic lipid A derivatives show that some of them stand out as promising, new immunoadjuvant candidates.  相似文献   
180.
Complex [Ti(κ2N,O‐{2,6‐F2C6H3N?C(Me)C(H) ?C(CF3) O})2Cl2] ( 1 ) was evaluated as catalyst for living copolymerization of ethylene (E) with norbornene (N) upon activation with dried methylaluminoxane (d‐MAO) at temperatures between 25 and 90 °C. Copolymerization performed at different [N]/[E] feed ratios afforded stereoirregular alternating high molar mass P(E‐co‐N) with narrow molar mass distribution. The living nature of E‐co‐N copolymerization by 1 /d‐MAO was demonstrated by kinetics at 50 °C. This catalyst system was used for the synthesis of block copolymers such as polyethylene (PE)‐block‐P(E‐co‐N) with a crystalline PE block and an amorphous P(E‐co‐N) block as well as P(E‐co‐N)1block‐P(E‐co‐N)2, having different norbornene contents in the segments and thus having different Tg values. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号